Diseases of the spine cause significant morbidity. These diseases include abnormalities of the vertebrae, the intervertebral discs, the facet joints, and connective tissue around the spine. These abnormalities can be caused by a number of factors, including mechanical injury or degenerative disc disease. Such abnormalities can cause instability to the spine, vertebral misalignment, and abnormal motion between adjacent vertebrae. More severe disease may result in wear to the vertebral bony surfaces or cause nerve compression, and may ultimately produce severe pain. Further, these conditions are often chronic and progressive problems.
The treatments for spinal disorders may include long-term medical management or surgery. Medical management is generally directed at controlling the symptoms, such as pain, rather than correcting the underlying problems. For some patients this may require chronic use of pain medications, which may alter patient mental state or cause other negative side effects.
Another treatment option is surgery, which is often highly invasive and may significantly alter the spinal anatomy and function. For example, one surgical treatment for certain spinal conditions includes spinal fusion, whereby two or more vertebrae may be joined using bone grafts and/or synthetic implants. Fusion is irreversible and may significantly alter vertebral range-of-motion. Further, current surgical procedures are often only applicable to patients in a significantly progressed disease state.
Consequently, spinal surgeons have begun to develop more advanced surgical procedures and spinal stabilization and/or repair devices that are less invasive, may be reversible, and cause a less drastic alteration in the patient's normal anatomy and spinal function. These procedures may be used in an earlier stage of disease progression and, in some situations, may even stop or reverse disease progression.
Many devices and procedures that are designed to treat the spine or other body structures require bone-anchoring elements, which may include screws, pins, or nails. These bone-anchoring elements may connect one or more vertebrae with components of a treatment system. For example, pedicle screws are often used to connect spinal rods and/or plates to one or more vertebrae to facilitate fusion, correct a deformity, fix a fracture, and/or for a variety of other suitable treatment methods.
For some surgical procedures and implants, it is desirable to use a bone-anchoring element that can be implanted in a variety of configurations. For example, it is often desirable to use bone screws that can be fixed to bone at a range of suitable angles and still be properly connected with other components of an integrated treatment system.
Recently, spinal surgeons have begun to develop more dynamic treatment systems. Such systems may provide a certain degree of limited but controlled movement and may provide improved care for patients suffering from a variety of disorders including, for example, scoliosis and degenerative disc disease. These systems may benefit from improved bone-anchoring elements, including polyaxial screws.